# std::hash<std::filesystem::path>

From cppreference.com
< cpp‎ | filesystem‎ | path

Defined in header `<filesystem>` |  |
template<> struct hash<std::filesystem::path>; |  | (since C++17)

The template specialization of std::hash for std::filesystem::path allows users to obtain hash values of std::filesystem::path.

The operator() of this specialization is noexcept. For every std::filesystem::path value `p`, std::hash<std::filesystem::path>{}(p) is equal to std::filesystem::hash_value(p).

This specialization was absent from the C++17 standard publication, see LWG issue 3657.

### Example

Run this code

    #include <cassert>
    #include <cstddef>
    #include <filesystem>
    #include <iomanip>
    #include <iostream>
    #include <unordered_set>
    namespace fs = std::filesystem;

    void show_hash(fs::path const& p)
    {
        std::cout << std::hex << std::uppercase << std::setw(16)
                  << std::hash<fs::path>{}(p) << " : " << p << '\n';
    }

    int main()
    {
        auto tmp1 = fs::path{"/tmp"};
        auto tmp2 = fs::path{"/tmp/../tmp"};
        assert(!(tmp1 == tmp2));
        assert(fs::equivalent(tmp1, tmp2));
        show_hash(tmp1);
        show_hash(tmp2);

        for (auto s : {"/a///b", "/a//b", "/a/c", "...", "..", ".", ""})
            show_hash(s);

        std::unordered_set<fs::path, std::hash<fs::path>> dirs{
            "/bin", "/bin", "/lib", "/lib", "/opt", "/opt", "/tmp", "/tmp/../tmp"};
        for (fs::path const& p : dirs)
            std::cout << p << ' ';
        std::cout << '\n';
    }

Possible output:

    6050C47ADB62DFE5 : "/tmp"
    62795A58B69AD90A : "/tmp/../tmp"
    FF302110C9991974 : "/a///b"
    FF302110C9991974 : "/a//b"
    FD6167277915D464 : "/a/c"
    C42040F82CD8B542 : "..."
    D2D30154E0B78BBC : ".."
    D18C722215ED0530 : "."
                   0 : ""
    "/tmp/../tmp" "/opt" "/lib" "/tmp" "/bin"

### See also

hash (C++11) | hash function object (class template)
hash_value (C++17) | calculates a hash value for a path object (function)

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